Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh31b..05k&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SH31B-05
Physics
7807 Charged Particle Motion And Acceleration, 2114 Energetic Particles, Heliospheric (7514), 2151 Neutral Particles, 2154 Planetary Bow Shocks
Scientific paper
We report on data from the LECP (Low Energy Charged Particle) instruments on Voyagers 1 and 2. Our focus is on observations in the outer heliosphere of low-energy oxygen ions with energies in the ranges (1) ≈4-16 keV/nuc and (2) ≈130-250 keV/nuc. The lower energy component (1) is detected as a result of being boosted by solar wind convection into the sunward looking sector of thin solid-state detector. The higher energy component (2) is identified by careful corrections of rate channel data. We concentrate on the solar inactive periods ≈1984-1986 and ≈1995-1998. It is during these periods that component (1) is most easily detected because during solar minima the solar wind speed tends to be higher and interplanetary proton intensities, which reduce instrumental sensitivity for detecting the convected oxygen ions, tend to be lower. We have interpreted component (1) as pickup oxygen ions having speeds up to few times the solar wind speed, i.e., in the low-energy portion of the high-energy tail of the pickup ion distribution. During 1996-1997, the three-point intensity spectrum at Voyager 1, which covers 6.3-16.3 keV/nuc oxygen, is consistent with a model wherein pickup oxygen ions are stochastically accelerated to form the high-energy tail, which deceases exponentially with energy. However, component (2), which is at an energy well below the low-energy turnover of anomalous cosmic ray oxygen, has an intensity that lies far above the model-predicted tail. In fact, a simple linear fit to components (1) and (2) is consistent with an oxygen ion intensity that decreases with energy as a power law with a power law index ≈2. This result is remarkably similar in form to the high-energy tails observed over a broad energy range at ACE. We will report on our progress in enlarging our data sets and in interpreting the results and their implications for acceleration processes in the solar wind.
Armstrong Thomas P.
Decker Robert B.
Gloeckler George
Hamilton Douglas C.
Krimigis Stamatios M.
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